The study of the purity of the melt in the process of casting aluminum alloys of the Al-Zn- Mg-Cu system by the PoDFA method revealed a rather high content of spinel AlMg2O4 [1-3]. The presence of spinel was also found in the study of defects detected by ultrasonic testing of deformed semi-finished products. X-ray microspectral analysis of defects detected in semi-finished products from alloys of the Al-Mg and Al-Zn-Mg-Cu systems, as well as used ceramic foam filters, showed that the main reason for the appearance of spinel ingots is the interaction of the melt with the material of the ceramic foam filter.